Do you really need a pre-race caffeine detox?

US Olympic marathoner Desiree Linden, as her Twitter bio proclaims, is a coffee aficionado. At a sports nutrition conference a few years ago where she appeared as a guest, I remember the topic of pre-race coffee came up. One of her least favorite things about racing, she said, was having to give up coffee in the week leading up to the race in order to maximise the performance boost from a pre-race dose of caffeine.

This strategy is pretty common among coffee-drinking elite runners. But whether it’s really necessary has long been debated, with a few small studies producing conflicting findings on either side.

So a new study in the Journal of Applied Physiology, from researchers led by Bruno Gualano at the University of São Paulo, set out to test the question with the biggest and most rigorously designed study yet.

The study put 40 well-trained cyclists through a series of three time trials lasting about 30 minutes, while taking nothing, a placebo, or a dose of caffeine (6 milligrams per kg of body weight) an hour before the trial. They abstained from caffeine for 24 hours leading up to each trial.

Based on dietary recall data, the subjects were divided in low (2 to 101 mg/day), moderate (104 to 183 mg/day), and high (190 to 583 mg/day) caffeine groups. (By way of comparison, a medium-size cup of Starbucks Pike Place Roast filter coffee has about 310 mg of caffeine.) The researchers expected that the low-caffeine group would see the biggest performance boost, while the high-caffeine group would see a smaller boost because (without an abstinence period) they would have built up a higher tolerance to the effects of caffeine.

As the researchers point out, there are lots of theories for why caffeine seems to be such a reliable performance booster, including changes to fat oxidation and muscle function. But the dominant theory is that it blocks adenosine receptors in the brain, leading to higher levels of dopamine and noradrenaline, which “promotes feelings of wakefulness and alertness, and decreases the rate of perceived exertion and pain during exercise.” It’s the feeling that matters, in other words.

They did, indeed, find that caffeine boosted performance. When caffeinated, the cyclists went 2.5 percent faster, on average, compared to the placebo condition, and 3.3 percent faster than the no-supplement control condition. Having both a placebo and a control ride is nice, because it gives a sense of the magnitude of the placebo effect in these particular cyclists under these particular conditions.

The surprise: There was no difference between the caffeine groups. The habitual caffeine users were just as likely to get a boost as the low-caffeine consumers.

A few details to note. If you subscribe to the “forget statistics, let’s just squint at the graph” school of scientific analysis, you might argue that there are some subtle differences. Here’s what the time trial results look like for each group under each condition:

You might argue that the high-caffeine group looks to have a slightly smaller boost in the caffeine condition than the other two. But check out the error bars: If there’s any difference, it’s minuscule and unlikely to have any practical significance.

More interesting is the role of individual variation. Overall, about half the cyclists saw a caffeine-fuelled boost that was greater than the natural variation in repeated time trial results, which according to the study is about 3 percent. The other half mostly saw indeterminate results, with a small number (four) seeing negative results by more than 3 percent.

That’s consistent with results presented at last year’s American College of Sports Medicine meeting, which found that caffeine boosts performance for most people, but doesn’t help some and may even slow down a few. The variation in that case had nothing to do with habitual caffeine consumption and instead depended on certain gene variants that influence how quickly you metabolise caffeine.

It’s tempting to speculate that the same thing is going on in the new study, though they didn’t do genetic testing to test this idea.

For now, the conclusion is that Des Linden and other runners should feel free to keep drinking their coffee in the lead-up to races. After all, going cold-turkey is not without side effects, and pre-race nerves are bad enough without inflicting an unnecessary mood-altering hardship on yourself.

But keep in mind that this is yet another study suggesting that, even though caffeine is a reliable performance booster on average, only about half of individuals seem to see a robust performance gain. So if you have the sense that caffeine doesn’t seem to help you, you may be right.

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